How to sort 3D models, like adding tags to them, and select 3D by tags?
Thanks to Mr Zak, Ray Mairlot, and Duarte Farrajota Ramos
Grouping elements is a way to work, and using Blender Groups as Layers is definitively a good workaround of tags to organize the work

Ctrl+G to create group
Shift+G to select similar groups
Ctrl+Shift+G to add selection to selected object group
Ctrl+Alt+G to remove selected object from all groups he is in - How to remove object from group?


If you add an object to a group you can select by that group via Shift+G menu or view groups in the Outliner. – Mr Zak
You group objects by selecting them and pressing Ctrl+G. It doesn't create any extra hierarchy. – Ray Mairlot

Thanks to you two, I didn't know about group and I now understand better what a group is and how to use it. Also I found here ; https://blenderartists.org/forum/showthread.php?181779-SOLVED-Add-several-objects-to-existing-group that using Shift+Ctrl+G is the way to add object to an existing group – LeDucSAS

Using Blender Groups as Layers is a good way to organize a scene. Each object can belong to any number of groups at the same time, essentially working like 'tags'. Set the outliner permanently to Groups view so you can toggle visibility and selectability easily. – Duarte Farrajota Ramos